BC-1g plate choke

[k7mdo]

Does anyone have an estimate for the required plate choke milihenries in my conversion to 3870?


I have read the issues involve resonance at 3870 being an issue along with current handling capability.

Thanks, Tom

[KD6VXI]

It's the combo of mH and distributed C that cause resonance.

GDO it (or use a VNA (my method)) of the choke in place and see where you have any resonance. W8JI also describes a method using a transceiver, though I've not done that

Since the TX was designed for lower in operation, remove some turns until the resonance moves above 75 meters.

But, no, I'm not sure what amount you'll need.  I use Xl 10x my plate impedance as a minimum.

--Shane
KD6VXI

[k7mdo]

Shane, I was hoping there might be someone else who has done the same and knows the choke I might need....  I'm not adverse to using your technique though, just lazy.

That transmitter is taking up a lot of room in the shack and it needs to get done!!

Tom

[KD6VXI]

1.16 mH is what I came up with.

This was done:

Plate Voltage
2550

Plate Current
.550

(.6XPlateV)/Plate I


(2550*.6)/.550 = 2800 Ohms

Multiply that by 10 and you have 28K

XL = 2piFL
     = 2 x 3.141592653 x 3.870 MHz x 1.16 mH
     = 2.82E+04 ohms (to 3 significant digits)
     = 28,206 ohms


Hope that helps bud.  Maybe remove enough turns to get you to that point.


--Shane
KD6VXI

(Edit:  I used the resting voltage on the BC1G listed in the manual for the transmitter.  Since that doubles along with current, the plate impedance should stay close to the same.  Also, this was done for 1Kw output.  Who runs 250 watts?    Although the 250 watts shouldn't be much difference since the plate voltage and current will both drop by half at carrier)

[ka1shu.]

shane how about for 11m

[KD6VXI]

Good luck getting it to play anywhere above 40.

Some have said they had problems getting them on 40.

Your comment was to tongue in cheek, I'm sure.

Besides, it's called extended 10 meters.

😂😁

--Shane
KD6VXI

[k7mdo]

Many thanks!  That will get me started!  Appreciate all the help.

73 Tom

[KD6VXI]

Tom,

No problem.

Transformer is perfect, I'll put the Czech in the mail 👌😊👍

--Shane
KD6VXI

[k7mdo]

(.6XPlateV)/Plate I

I am really novice at this but everything you did seems clear BUT why the (.6) in the formula above?

Tom

[KD6VXI]

It's called the K factor.

Since the anode doesn't conduct 100 pct of the rf cycle you have to take it into account.

On a class C final you could probably up it to .7 or 8.... 

On another note, xformer showed up yesterday.  Very quick!  Have a check to you this weekend bud.

--Shane
KD6VXI

[k7mdo]

Thanks, Tom